1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling logged minimization of drive tests (MDT) reporting in a wireless communication system and related communication device.
2. Description of the Prior Art
The 3rd Generation Partnership Project (3GPP) has developed a universal mobile telecommunications system (UMTS) which adopts a wideband code division multiple access (WCDMA) as a wireless air interface. In the UMTS, a radio access network known as a universal terrestrial radio access network (UTRAN) includes multiple Node-Bs (NBs) for communicating with multiple user equipments (UEs). The WCDMA provides high frequency spectrum utilization, universal coverage, and high-speed multimedia data transmission which are beneficial for the UEs and the NBs of the UMTS. Furthermore, a long-term evolution (LTE) system is now being developed by the 3GPP as a successor of the UMTS, to further enhance performance of the UMTS to satisfy users' increasing needs. The LTE system includes a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved UTRAN (E-UTRAN) includes multiple evolved NBs (eNBs) for communicating with multiple UEs, and communicates with a core network including a mobility management entity (MME), serving gateway, etc for NAS (Non Access Stratum) control.
For a wireless communication system (e.g. the UMTS or the LTE system) to be seamless to a UE such that the UE can be covered everywhere without experiencing call drops or receiving severely faded signals, NBs of the wireless communication system must be deployed properly. However, to deploy the NBs properly, an operator of the wireless communication system must spend many human and material resources in measurements such that optimizations and plannings on deploying the NBs can be performed based on measurement results. The measurements may be performed on strength or quality of signals at certain times and geographical locations which are helpful to deploying the NBs. Therefore, it may be economical to exploit a UE of the wireless communication which is capable of performing the measurements and reporting the measurement results to a NB serving the UE. Accordingly, when more and more UEs can perform the measurements and reporting the measurement results to corresponding NBs, the operator can exploit the measurement results reported by the UEs to perform the optimizations and the plannings on deploying the NBs without spending many human and material resources.
The logged minimization of drive tests (MDT) is proposed to realize the above illustration with the minimized impact on operation and power consumption of the UE. According to the logged MDT, a UE stores measurements performed in an idle mode, and reports the stored measurements (or called MDT logs) to a NB serving the UE when the UE transfers to a connected mode due to a normal event (e.g. a voice call or data call). In other words, the UE will not consume power for transferring to the connected mode to report the MDT logs to the NB, but only report the MDT logs to the NB when the UE is triggered by the normal event to transfer to the connected mode. Therefore, the operator can obtain the MDT logs from the UE via the NB, and the impact to the operation and the power consumption of the UE is minimized at the same time.
However, a size of the MDT logs is usually large, and the UE requires a period of time to finish reporting the MDT logs. Therefore, it is possible that the reporting of the MDT logs is interrupted when the UE is reporting the MDT logs to the NB. For example, the UE may intend to release a connection between the UE and the NB such that the UE can transfer to the idle mode to reduce the power consumption, when the UE finishes receiving services from the NB. To release the connection, the UE can initial a connection release procedure by sending a Signalling Connection Release Indication (SCRI) message to the NB. In this situation, the reporting of the MDT logs is interrupted, and the NB loses MDT logs which have not been received. It is not known whether the NB can continue to receive the MDT logs not received, when the UE transfers back to the connected mode. Therefore, how to handle reporting of the MDT logs when the UE intends to release the connection between the UE and the NB is a topic to be discussed and addressed.